The real effect is smaller because electrons scatter somewhat from both layers.

The first was to use a thinner resist layer, to minimize electron scattering.

However, the scattered light is extremely weak and therefore yields a very low signal.

In this scenario, all the electrons eventually scatter during their long trip along the sandwich: the spin-up electrons from one iron layer and the spin-down electrons from the other.

We can more or less guess at the time and how long it might survive before it's either captured, scattered or absorbed.